1. Field of the Invention
This invention relates to a polarizing element from which incident light having random polarization direction components emerges with the polarization direction uniformized, and a projector using such polarizing element.
2. Related Background Art
There is known a projector of the construction as shown in FIG. 1 of the accompanying drawings.
A light beam emitted from a light source 1550 is separated into red, green and blue lights by dichroic mirrors 1551 and 1552, and the red, green and blue lights are directed to liquid crystal light bulbs 1554, 1555 and 1556, respectively, by the use of a total reflection mirror 1553 and further, the optical paths of these lights are bent by a total reflection mirror 1557, and the three red, green and blue images are combined by dichroic mirrors 1558 and 1559 and the combined image is projected onto a screen, not shown, by a projection lens 1560.
Such a projector adopts a construction in which the liquid crystal light bulbs 1554, 1555 and 1556 assume a form in which a liquid crystal plate is interposed between two polarizing plates which are polarizing elements and when natural light having random polarization directions enters the incidence side polarizing plate, polarized lights in the other polarization directions than one polarization direction are absorbed by said incidence side polarizing plate and only the light in one polarization direction enters the liquid crystal plate.
On the other hand, the projector described in Japanese Patent Laid-Open Application No. 61-90584 adopts a construction in which the incidence side polarizing plate is eliminated and instead, by the use of a prism and a beam splitter which is a polarizing element, light is caused to enter a liquid crystal plate with the polarization directions thereof uniformized in one direction.
However, the projector shown in FIG. 1 suffers from the problem that lights in the other polarization directions than the polarization direction of the polarized light transmitted through the incidence side polarizing plate are absorbed by the incidence side polarizing plate and therefore the projection image field becomes dark, and further suffers from the problem that the temperature of the liquid crystal plate is increased by the absorbed lights, thus resulting in the deterioration of the liquid crystal plate.
On the other hand, in the projector described in Japanese Patent Laid-Open Application No. 61-90584, the use of the polarizing beam splitter and the prism leads to the bulkiness of the apparatus and moreover, there is the problem that labor and cost are required for the polarizing of the prism. Also, the use of a glass block such as a prism leads to too great a weight, which in turn leads to bad portability as a projector.